U.S. patent application number 13/639888 was filed with the patent office on 2013-02-21 for combustion control apparatus for an internal combustion engine.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is Naoya Kaneko. Invention is credited to Naoya Kaneko.
Application Number | 20130042611 13/639888 |
Document ID | / |
Family ID | 44762194 |
Filed Date | 2013-02-21 |
United States Patent
Application |
20130042611 |
Kind Code |
A1 |
Kaneko; Naoya |
February 21, 2013 |
COMBUSTION CONTROL APPARATUS FOR AN INTERNAL COMBUSTION ENGINE
Abstract
An object of this invention is to provide a technology wherein a
stratification of an EGR gas with an air-fuel mixture or a fresh
air is achieved and capable of introducing the EGR gas in a large
quantity, even when an engine load is high as an operation state of
an internal combustion engine. With this invention, when a
stratified combustion is performed by introducing the EGR gas, the
fresh air is supercharged by a compressor, a fresh air blocking
valve is closed to block inflow of the fresh air into a first
intake port, and a variable valve mechanism opens a first intake
valve before opening of a second intake valve, and, thereafter,
opens the second intake valve.
Inventors: |
Kaneko; Naoya; (Susono-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kaneko; Naoya |
Susono-shi |
|
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
|
Family ID: |
44762194 |
Appl. No.: |
13/639888 |
Filed: |
April 8, 2010 |
PCT Filed: |
April 8, 2010 |
PCT NO: |
PCT/JP2010/056394 |
371 Date: |
October 8, 2012 |
Current U.S.
Class: |
60/605.2 ;
123/559.1 |
Current CPC
Class: |
F02D 13/0257 20130101;
F02D 13/0226 20130101; F02D 2041/001 20130101; F02M 26/07 20160201;
F02B 17/00 20130101; F02D 41/0057 20130101; F02D 13/0269 20130101;
F02D 41/3023 20130101; Y02T 10/40 20130101; F02D 41/0007 20130101;
F02M 26/20 20160201; Y02T 10/12 20130101; F02D 21/08 20130101; F02B
2023/108 20130101; F02B 2031/006 20130101; F02D 13/02 20130101 |
Class at
Publication: |
60/605.2 ;
123/559.1 |
International
Class: |
F02M 25/07 20060101
F02M025/07; F02B 37/00 20060101 F02B037/00; F02B 33/00 20060101
F02B033/00 |
Claims
1. A combustion control apparatus for an internal combustion engine
comprising: a first intake passage and a second intake passage
respectively and independently connected with a combustion chamber
of the internal combustion engine, and which supply an intake air
to the combustion chamber; an EGR apparatus that circulates an EGR
gas comprising apart of an exhaust gas into an EGR gas supply port
provided at the first intake passage, from an exhaust passage of
the internal combustion engine; a fresh air blocking unit that
blocks inflow of fresh air to the first intake passage; a
supercharger that supercharges fresh air at the upstream of the
first intake passage and the second intake passage; an opening and
closing property changing unit that differentiates the timing of
opening of a valve between a first intake valve that controls the
intake air which inflows into the combustion chamber from the first
intake passage, and a second intake valve that controls intake air
which inflows into the combustion chamber from the second intake
passage; and a control unit that, when the EGR gas is introduced
and subjected to stratified combustion, controls to supercharge the
fresh air by the supercharger, to block inflows of the fresh air
into the first intake passage by the fresh air blocking unit, to
open the first intake valve before opening of the second intake
valve by the opening and closing property changing unit, and,
thereafter, to open the second intake valve.
2. The combustion control apparatus for the internal combustion
engine according to claim 1, wherein the control unit increases a
supercharging pressure for supercharging the fresh air by the
supercharger to a pressure higher than an inner pressure of a
cylinder of the internal combustion engine between a period from
closing of the first intake valve to closing of the second intake
valve.
3. The combustion control apparatus for the internal combustion
engine according to claim 1, wherein the supercharger is a
turbocharger, and the EGR apparatus comprises an EGR passage which
connects the exhaust passage at the downstream of a turbine of the
turbocharger with the EGR gas supply port.
4. The combustion control apparatus for the internal combustion
engine according to claim 1, wherein the first intake passage and
the second intake passage are each a helical port or a tangential
port to form the intake air flowed into the combustion chamber in
the form of a swirl flow in the same direction.
5. The combustion control apparatus for the internal combustion
engine according to claim 1, wherein the control unit controls, at
the time of performing a stratified combustion where an EGR gas is
introduced and when the intake air flowing through the second
intake passage is allowed to flow into the combustion chamber in a
compression stroke, to supercharge the fresh air by the
supercharger, to block inflows of the fresh air into the first
intake passage by the fresh air blocking unit, to open the first
intake valve before opening of the second intake valve, and,
thereafter, to open the second intake valve, by the opening and
closing property changing unit, or the control unit controls, when
it is not required to have the intake air flowing through the
second intake passage flow into the combustion chamber in the
compression stroke, to not supercharge the fresh air by the
supercharger, to block inflow of the fresh air into the first
intake passage by the fresh air blocking unit, to open the first
intake valve before opening of the second intake valve, and,
thereafter, to open the second intake valve, by the opening and
closing property changing unit.
6. The combustion control apparatus for the internal combustion
engine according to claim 1, wherein the fresh air blocking unit
switches the intake air to flow through the first intake passage to
either the fresh air inflows from the upstream of the first intake
passage or the EGR gas inflows from the EGR gas supply port.
7. The combustion control apparatus for the internal combustion
engine according to claim 6, wherein a volume of the first intake
passage from the fresh air blocking unit to the combustion chamber
is substantially equal to a quantity of the EGR gas supplied to the
combustion chamber when the stratified combustion is performed by
introducing the EGR gas in an operation state of either in a state
where an engine load is high or in a state where an engine
revolution speed is high; the control unit, when switching is made
from the stratified combustion to a non-stratified combustion where
a requesting torque is high and the EGR gas is not introduced,
switches the intake air to flow through the first intake passage to
a fresh air inflows from the upstream of the first intake passage,
by the fresh air blocking unit at the time when the cylinder, which
entered into an intake stroke first after the switching request,
starts to flow the intake air into the combustion chamber, and,
thereafter, from the time when the cylinders, other than the
first-mentioned cylinder have completed to flow the intake air into
the combustion chamber at the first one cycle, the opening and
closing properties of the first intake valve and the second intake
valve are changed by the opening and closing property changing
unit.
8. The combustion control apparatus for the internal combustion
engine according to claim 1, wherein the control unit controls, at
the time of performing the non-stratified combustion in a state of
low engine load where the EGR gas is not introduced, to have the
opening closing property changing unit maintain the first intake
valve in the closed state.
Description
TECHNICAL FIELD
[0001] The present invention relates to a combustion control
apparatus for an internal combustion engine that effects stratified
combustion in which an EGR gas with an air-fuel mixture or fresh
air is stratified (layered) in a combustion chamber.
BACKGROUND ART
[0002] There exist EGR apparatuses for circulating a part of an
exhaust gas of an internal combustion engine as the EGR gas. With
the supply of the EGR gas together with an air-fuel mixture or
fresh air to the combustion chamber, decreasing of NOx in the
exhaust gas and improving fuel consumption are intended. A
technology is known in which the EGR gas with the air-fuel mixture
or fresh air is stratified (layered) in the combustion chamber in
order to increase the quantity of the EGR gas supplied to the
internal combustion engine.
[0003] In Patent Document 1, timings of opening and closing of two
intake valves are staggered from each other by an opening and
closing property changing unit, thereby to cause the EGR gas to
flow first into the combustion chamber from an intake port having a
swirl control valve, and, thereafter, to cause fresh air to flow
into the combustion chamber from the other intake port. Whereby in
the combustion chamber, stratification of the EGR gas and fresh air
is achieved in which the layer of the EGR gas is a lower layer and
the layer of fresh air is an upper layer.
PRIOR ART DOCUMENTS
Patent Documents
[0004] Patent Document 1: Japanese Patent Application Laid Open
Publication No. 2004-144052
[0005] Patent Document 2: Japanese Patent Application Laid Open
Publication No. 06(1994)-200836
[0006] Patent Document 3: Japanese Patent Application Laid Open
Publication No. 63(1988)-162933
SUMMARY OF THE INVENTION
The Problems to be Solved by the Invention
[0007] With the technology of Patent Document 1, when an engine
load is high as the operation state of the internal combustion
engine, fresh air is introduced through both intake ports, and an
opening degree of an EGR valve is made smaller thereby to secure
the intake quantity supplied to the internal combustion engine.
However, in this manner, the EGR gas and fresh air cannot be
stratified, and, further, the EGR gas in a large quantity cannot be
introduced. As a result, with the technology of Patent Document 1,
when the engine load was high as mentioned above, it was not
possible to achieve decreasing the NOx in the exhaust gas or
improving the fuel consumption.
[0008] The present invention was made in view of the above stated
circumstances, and an object of the invention is to provide a
technology that, in a combustion control apparatus for an internal
combustion engine, even when an engine load is high as an operation
state of the internal combustion engine, an EGR gas with an
air-fuel mixture or fresh air is stratified, and, at the same, the
EGR gas in large quantity can be introduced.
Means for Solving the Problems
[0009] The present invention adopts the following structure. That
is, the present invention is a combustion control apparatus for an
internal combustion engine comprising:
[0010] a first intake passage and a second intake passage
respectively and independently connected with a combustion chamber
of the internal combustion engine, and which supply an intake air
to the combustion chamber;
[0011] an EGR apparatus that circulates an EGR gas comprising a
part of an exhaust gas into an EGR gas supply port provided at the
first intake passage, from an exhaust passage of the internal
combustion engine;
[0012] a fresh air blocking unit that blocks inflow of fresh air to
the first intake passage;
[0013] a supercharger that supercharges the fresh air at the
upstream of the first intake passage and the second intake
passage;
[0014] an opening and closing property changing unit that
differentiates the timing of opening of a valve between
[0015] a first intake valve that controls intake air which inflows
into the combustion chamber from the first intake passage, and
[0016] a second intake valve that controls intake air which inflows
into the combustion chamber from the second intake passage; and
[0017] a control unit that, when the EGR gas is introduced and
subjected to stratified combustion, controls to supercharge fresh
air by the supercharger, to block inflows of fresh air into the
first intake passage by the fresh air blocking unit, to open the
first intake valve before opening of the second intake valve by the
opening and closing property changing unit, and, thereafter, to
open the second intake valve.
[0018] Here, the expression of "when the EGR gas is introduced and
subjected to stratified combustion" refers to an operation state of
the internal combustion engine wherein the EGR gas is stratified
with the air-fuel mixture or fresh air in the combustion chamber,
thereby to decrease NOx in the exhaust gas and to improve fuel
consumption. The term "intake air" is the general term for fresh
air, air-fuel mixture and EGR gas which flow into the internal
combustion engine. The term "fresh air" refers to fresh air that is
supplied externally of the internal combustion engine. The term
"air-fuel mixture" refers to a gas comprising a mixture of fresh
air and fuel. The term "EGR gas" refers to an inactive gas that is
part of the exhaust gas discharged from the internal combustion
engine.
[0019] With the present invention, when the EGR gas is introduced
and subjected to stratified combustion, fresh air is supercharged
by the supercharger, inflow of fresh air into the first intake
passage is blocked by the fresh air blocking unit, the first intake
valve is opened before opening of the second intake valve by the
opening and closing property changing unit, and, thereafter, the
second intake valve is opened.
[0020] In this way, in which inflow of fresh air into the first
intake passage is blocked by the fresh air blocking unit, and the
first intake valve is opened before opening of the second intake
valve by the opening and closing property changing unit, thereby,
the EGR gas which flows through the first intake passage flows into
the combustion chamber, first. This EGR gas is descending while
forming a swirl flow in the combustion chamber. Thereafter, due to
opening of the second intake valve by the opening and closing
property changing unit, the air-fuel mixture or fresh air which
flows through the second intake passage flows into the combustion
chamber. This air-fuel mixture or fresh air constitutes a layer
formed by a swirl flow thereof above the EGR gas layer which flowed
into the combustion chamber, first. Whereby the stratification
comprising the EGR gas as the lower layer and the air-fuel mixture
or fresh air as the upper layer, can be achieved in the combustion
chamber.
[0021] When the engine load is high as the operation state of the
internal combustion engine, the EGR gas first inflows into the
combustion chamber, so that the air-fuel mixture or fresh air which
inflows after the EGR gas is difficult to flow into the combustion
chamber under a negative pressure due to descending of a piston
during an intake stroke. However, with the present invention, fresh
air is supercharged by the supercharger, so that the air-fuel
mixture or fresh air, which has been supercharged, can flow into
the combustion chamber not only during the intake stroke, but also
during a compression stroke. Whereby, even when the engine load is
high, stratification of the EGR gas and the air-fuel mixture or
fresh air can be achieved without deteriorating the intake
efficiency, and, at the same time, the EGR gas in large quantity
can be introduced.
[0022] Further, the air-fuel mixture or fresh air, which inflows
after the EGR gas, forms the swirl flow in the combustion chamber
during the latter half of the intake stroke, or during the
compression stroke. Because of this, the stratified state of the
combustion chamber can be easily maintained until ignition in the
combustion chamber, so that the effect provided stratification can
be exhibited to maximum extent.
[0023] The control unit may increase a supercharging pressure of
fresh air to be supercharged by the supercharger to a pressure
higher than a pressure in a cylinder of the internal combustion
engine during a period from closing of the first intake valve to
closing of the second intake valve.
[0024] In this way, the supercharged air-fuel mixture or fresh air
can flow into the combustion chamber without making a reverse flow
caused by being forcibly pushed back by the pressure in the
cylinder of the internal combustion engine.
[0025] The supercharger is a turbocharger, and the EGR apparatus
may comprise an EGR passage connecting the exhaust passage at
downstream from a turbine of the turbocharger and the EGR gas
supply port.
[0026] The ERG gas, which is a part of the exhaust gas from the
exhaust passage downstream of the turbine of the turbocharger, has
its temperature and pressure being dropped, because this EGR gas is
after having performed the work of driving the turbine. Here, this
EGR gas is introduced into the combustion chamber from the
beginning of the intake stroke under the negative pressure due to
descending of the piston during the intake stroke. At this time,
the sufficient negative pressure is secured so that even this EGR
gas with the dropped temperature and pressure can be sufficiently
supplied to the combustion chamber. By using this EGR gas, the rise
in the intake temperature can be suppressed and also lowering of
the charging efficiency caused by the high intake temperature can
be suppressed.
[0027] The first intake passage and the second intake passage may
be a helical port or a tangential port in which the intake air
flowed into the combustion chamber forms the swirl flow in the same
direction.
[0028] Whereby in the combustion chamber, the friction is difficult
to be produced at a boundary surface between the lower layer which
formed the swirl flow of the EGR gas flowed therein first and the
upper layer which formed the swirl flow of the air-fuel mixture or
fresh air above the lower layer, and it is difficult for the EGR
gas to mix with the air-fuel mixture or fresh air, the stratified
state can be maintained to the extent of greatest possible
degree.
[0029] The control unit, at the time when the EGR gas is introduced
and subjected to the stratified combustion, controls such that,
when the intake air which flows through the second intake passage
during the compression stroke is made to flow into the combustion
chamber, controls to supercharge the fresh air by the supercharger,
to block inflows of the fresh air into the first intake passage by
the fresh air blocking unit, to open the first intake valve by the
opening and closing property changing unit before opening of the
second intake valve, and, thereafter, to open the second intake
valve, or, when it is not necessary, during the compression stroke,
to have the intake air flowing through the second intake passage
flow into the combustion chamber, the control unit may control not
to supercharge the fresh air by the supercharger, control to block
inflow of the fresh air into the first intake passage by the fresh
air blocking unit, and to open the first intake valve before
opening of the second intake valve by the opening and closing
property changing unit, and thereafter, to open the second intake
valve.
[0030] As in the case where the engine load is high as the
operation state of the internal combustion engine, having the
intake air flowing through the second intake passage during the
compression stroke flow into the combustion chamber, it is required
to supercharge the fresh air by the supercharger. However, as in
the case where the engine load is low as the operation state of the
internal combustion engine, where it is not required, during the
compression stroke, to have the intake air flowing through the
second intake passage flow into the combustion chamber, it is
possible to have the air-fuel mixture or fresh air which inflows
after the EGR gas flow into the combustion chamber under the
negative pressure due to descending of the piston during the intake
air stroke. Hence, in the compression stroke, when it is not
necessary to have the intake air flowing through the second intake
passage flow into the combustion chamber, the fresh air is not
supercharged by the supercharger, so that the energy corresponding
to that might be used by the supercharger could be reduced from the
entire energy thereby to achieve energy saving.
[0031] The fresh air blocking unit may switch the intake air to
flow through the first intake passage to either the fresh air
inflows from the upstream of the first intake passage or the EGR
gas inflows from the EGR gas supply port.
[0032] In this manner, the EGR gas quantity can be controlled by
the timing of opening of the first intake valve and its lift
quantity, so that it is not required to provide an EGR valve in the
EGR apparatus. As a result, controlling of the EGR gas quantity can
be simplified, and, at the same time, the number of parts is
reduced by eliminating the EGR valve, so as to achieve a
cost-down.
[0033] Further, since controlling of the EGR gas quantity is
performed by the first intake valve, a distance between the part
which controls the EGR gas quantity and the combustion chamber
becomes zero, thereby there is no delay of response by the EGR gas,
whereby a misfire in the combustion engine and torque fluctuations
can be suppressed, and, hence, drivability can be stabilized.
[0034] A volume of the first intake passage from the fresh air
blocking unit to the combustion chamber is substantially equal to
the quantity of the EGR gas supplied to the combustion chamber when
making the stratified combustion by introducing the EGR gas in the
operation state of at least either in the state where the engine
load is high, or in the state where an engine revolution speed is
high, and
[0035] the control unit, when switching from the stratified
combustion to a non-stratified combustion where a requesting torque
is high and the EGR gas is not introduced, controls to switch the
intake air to flow through the first intake passage to the fresh
air inflows from the upstream of the first intake passage by the
fresh air blocking unit, when a cylinder, which first enters into
the intake stroke after the switching request, starts to flow the
intake air into the combustion chamber, and, thereafter, upon
completion of flowing the intake air into the combustion chamber in
the first one cycle of the cylinders other than the above-mentioned
cylinder, the opening and closing property of the first intake
valve and the second intake valve may be changed by the opening and
closing property changing unit.
[0036] Whereby, only the combustion of one complete cycle of all
cylinders after the switching request achieves the stratified
combustion, and, thereafter, the fresh air flows through the first
intake passage, thereby from the next and subsequent combustions
become the non-stratified combustion. Thus, the combustion shifts
from the stratified combustion to the non-stratified combustion
without substantially causing the response delay, the misfire in
the internal combustion engine, the torque fluctuations and
fluctuations in steps of torque.
[0037] The control unit, when the non-stratified combustion is made
in the state, where the engine load is low and the EGR gas is not
introduced therein, may maintain the first intake valve in the
closed state by the opening and closing property changing unit.
[0038] In this way, when the non-stratified combustion is made in
the state where the engine load of the internal combustion engine
is low and the EGR gas is not introduced therein, the second intake
valve, which is the other intake valve, is opened to allow the
air-fuel mixture or the fresh air to flow therein. Whereby, a
strong swirl is formed in the combustion chamber and the combustion
is stabilized.
[0039] Then, when the non-stratified combustion is switched to the
stratified combustion in which the EGR gas is introduced, the first
intake valve is opened to allow the EGR gas to flow therein from
the first intake passage, and also the second intake valve is
opened, the same as before the switching, to allow the air-fuel
mixture or the fresh air to flow into the combustion chamber. Since
thee is no change in the quantity of the air-fuel mixture or the
fresh air before and after the switching, shifting from the
non-stratified combustion to the stratified combustion can be
performed without causing fluctuations in the steps of torque.
Effects of the Invention
[0040] According to the present invention, in the combustion
control apparatus for an internal combustion engine, even when the
engine load is high as the operation state of the internal
combustion engine, the stratification of the EGR gas and the
air-fuel mixture or the fresh air can be achieved, and, at the same
time, the EGR gas can be introduced in a large quantity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] [FIG. 1] A diagram showing a schematic structure of an
internal combustion engine according to an Embodiment 1 of the
present invention.
[0042] [FIG. 2] A diagram showing a schematic structure of the
internal combustion engine according to the Embodiment 1 and its
intake system and exhaust system.
[0043] [FIG. 3] A diagram showing an example of valve timing of an
intake valve and an exhaust valve during the stratified combustion
and an internal pressure of a cylinder and a supercharger pressure
at that time according to the Embodiment 1.
[0044] [FIG. 4] A diagram showing a stratified state in the
combustion chamber according to the Embodiment 1.
[0045] [FIG. 5] A diagram showing an example of valve timing of the
intake valve and the exhaust valve during non-stratified combustion
according to the Embodiment 1.
[0046] [FIG. 6] A flowchart showing a combustion control routine of
the internal combustion engine according to the Embodiment 1.
[0047] [FIG. 7] A diagram showing a schematic structure of an
internal combustion engine according to another example of the
Embodiment 1 and its intake system and exhaust system.
[0048] [FIG. 8] A diagram showing a schematic structure of an
internal combustion engine according to another example of the
Embodiment 1.
[0049] [FIG. 9] A diagram showing the state wherein a helical port
or a tangential port is used for a first intake port and a second
intake port according to an Embodiment 2.
[0050] [FIG. 10] A diagram showing a stratified state in a
combustion chamber according to the Embodiment 2.
[0051] [FIG. 11] A diagram showing an example of valve timing of an
intake valve and an exhaust valve at the time of stratified
combustion when, in a compression stroke according to an Embodiment
3, it is not necessary to have an air-fuel mixture flowing through
a second intake port flow into a combustion chamber.
[0052] [FIG. 12] A diagram showing a schematic structure of an
internal combustion engine according to an Embodiment 4 and its
intake system and an exhaust system.
[0053] [FIG. 13] A diagram showing a pattern of selecting the
stratified combustion of the EGR gas and the air-fuel mixture, and
the non-stratified combustion where the EGR gas is not introduced,
whichever corresponds to an operation state of the internal
combustion engine according to the Embodiment 4.
[0054] [FIG. 14] A diagram showing a control timing when switching
is made from the stratified combustion to the non-stratified
combustion according to the Embodiment 4.
[0055] [FIG. 15] A diagram showing an example of valve timing of
the intake valve and the exhaust valve when switching is made from
the stratified combustion to the non-stratified combustion
according to the Embodiment 4.
[0056] [FIG. 16] A diagram showing an example of valve timing of
the intake valve and the exhaust valve at the time of
non-stratified combustion according to an Embodiment 5.
BEST MODES OF CARRYING OUT OF THE INVENTION
[0057] Hereinafter, a description will be made of specific
embodiments of the present invention.
Embodiment 1
[0058] (Internal Combustion Engine)
[0059] FIG. 1 is a diagram showing a schematic structure of an
internal combustion engine according to an Embodiment 1 of the
present invention. FIG. 2 is a diagram showing a schematic
structure of the internal combustion engine according to the
Embodiment 1 and its intake system and exhaust system. An internal
combustion engine 1 shown in FIG. 1 and FIG. 2 is a spark ignition
type four stroke cycle gasoline engine for driving a vehicle and
having four cylinders 2.
[0060] In each cylinder 2 of the internal combustion engine 1, a
piston 3 is slidably disposed. At the upper portion in the cylinder
2, a combustion chamber 4 is formed in a compartment by the upper
wall and the inner circumference wall of the cylinder 2 and the top
surface of the piston 3. At the upper portion of the combustion
chamber 4, connected thereto are a first intake port 5a and a
second intake port 5b, and a first exhaust port 6a and a second
exhaust port 6b. The first intake port 5a and the second intake
port 5b are independently and respectively connected to the
combustion chamber 4 to supply an intake air to the combustion
chamber 4. The first exhaust port 6a and the second exhaust 6b
discharge an exhaust gas after performing combustion in the
combustion chamber 4. A spark plug 7 is arranged at the center of
the upper portion of the cylinder 2 for performing ignition of the
air-fuel mixture in the combustion chamber 4.
[0061] An opening into the combustion chamber 4 of the first intake
port 5a in the upper wall of the cylinder 2 is opened and closed by
a first intake valve 8a. An opening into the combustion chamber 4
of the second intake port 5b in the upper wall of the cylinder 2 is
opened and closed by a second intake valve 8b. Further, an opening
into the combustion chamber 4 of the first exhaust port 6a is
opened and closed by a first exhaust valve 9a. An opening into the
combustion chamber 4 of the second exhaust port 6b in the upper
wall of the cylinder 2 is opened and closed by a second exhaust
valve 9b.
[0062] The first intake valve 8a and the second intake valve 8b
each is provided with a variable valve mechanism 10 which varies an
opening and closing property of each intake valve. This variable
valve mechanism 10 continuously varies a period of time of valve
opening (lift quantity), which is the opening and closing property
of each intake valve, and, at the same time, varies continuously a
opening and closing timing (valve timing) which is the opening and
closing property of each intake valve. The valve timings of the
first intake valve 8a and the second intake valve 8b may be
differentiated from one another by the variable valve mechanism 10.
The variable valve mechanism 10 of the present Embodiment
corresponds to the opening and closing property changing unit of
the present invention.
[0063] The first intake port 5a and the second intake port 5b
respectively include a first and a second fuel injection valves 11a
and 11b which inject a fuel toward the intake air flowing through
each intake port. The first intake port 5a, which is located at the
upstream of the first fuel injection valve 11a, is provided with an
EGR gas supply port 12. The first intake port 5a, which is located
at the upstream of the EGR gas supply port 12, is provided with a
fresh air blocking valve 13. The fresh air blocking valve 13, when
closed, blocks inflow of the fresh air into the first intake port
5a from the upstream. The fresh air blocking valve 13 of the
present Embodiment corresponds to the fresh air blocking unit of
the present invention. The upstream of the first intake port 5a
which is upstream of the fresh air blocking valve 13, and of the
second intake port 5b which is upstream of the second fuel
injection valve 11b, constitutes one intake pipe 14. The first
intake port 5a of the present Embodiment corresponds to the first
intake passage of the present invention. The second intake port 5b
of the present Embodiment corresponds to the second intake passage
of the present invention.
[0064] Further, the downstream of the first exhaust port 6a and of
the second exhaust port 6b constitutes one exhaust pipe 15.
[0065] At the midway of the intake pipe 14, there is provided a
compressor 16a of a turbocharger 16. At the midway of the exhaust
pipe 15, there is provided a turbine 16b of the turbocharger 16.
The turbocharger 16 is a supercharger that supercharges the fresh
air, in which the turbine 16b is rotated by utilizing the energy of
the exhaust gas flowing through the exhaust pipe 15, and the
compressor 16a is driven with the rotating force of the turbine
16b. The turbine 16b is provided with a waste gate valve 16c which
adjust an inflow quantity of the exhaust gas flowing into the
turbine 16b.
[0066] The intake pipe 14 at the upstream of the compressor 16a is
provided with a throttle valve 17. By this throttle valve 17, a
quantity of the fresh air flowing through the intake pipe 14 is
adjusted. The throttle valve 17 is controlled to open and close by
an electric actuator.
[0067] The intake pipe 14 at the downstream of the compressor 16a
is provided with an inter-cooler 18. The inter-cooler 18 cools the
fresh air flowing through the intake pipe 14 by performing a heat
exchange with the outside air. The intake pipe 14 at the downstream
of the inter-cooler 18 is provided with a surge tank 19. The surge
tank 19 temporarily stores therein the fresh air flowing through
the intake pipe 14. The surge tank 19 is provided with a pressure
sensor 20 which detects a pressure of the fresh air in the surge
tank 19. The intake pipe 14 at the downstream of the surge tank 19
is branched into the first intake port 5a and the second intake
port 5b.
[0068] The exhaust pipe 15 at the downstream of the turbine 16b is
provided with an oxidation catalyst 21 which serves as a start
catalyst.
[0069] The internal combustion engine 1 is provided with an EGR
apparatus 22. The EGR apparatus 22 comprises an EGR passage 23, an
EGR valve 24 and en EGR cooler 25.
[0070] One end of the EGR passage 23 is connected with the exhaust
pipe 15 at the downstream of the oxidation catalyst 21, and the
other end is connected with the EGR gas supply port 12 of the first
intake port 5a. The EGR apparatus 22, by causing the EGR gas to
flow through the EGR passage 23, circulates the EGR gas, which is a
part of the exhaust gas, into the EGR gas supply port 12 provided
in the first intake port 5a, from the exhaust pipe 15 of the
internal combustion engine 1.
[0071] The EGR valve 24 and the EGR cooler 25 are provided in the
EGR passage 23. A quantity of the EGR gas, which is introduced into
the first intake port 5a from the exhaust pipe 15 after passing
through the EGR passage 23, is adjusted by the EGR valve 24. The
EGR cooler 25 cools the EGR gas flowing through the EGR passage 23
by performing the heat exchange with a cooling water of the
engine.
[0072] The internal combustion engine 1 structured as described
above is provided with an electronic control unit (hereinafter will
be called "the ECU") 26 as an annex. A crank position sensor 27 and
an accelerator opening degree sensor 28 are electrically connected
to the ECU 26. Output signals from these sensors are inputted into
the ECU 26. The crank position sensor 27 is a sensor which detects
a crank angle of the internal combustion engine 1. Further, the
accelerator opening degree sensor 28 is a sensor which detects the
accelerator opening degree of a vehicle mounted with the internal
combustion engine 1.
[0073] Still further, the ECU 26 is electrically connected with the
variable valve mechanism 10, the first and the second fuel
injection valves 11a and 11b, the fresh air blocking valve 13, the
throttle valve 17 and the EGR valve 24. These are controlled by the
ECU 26.
[0074] (Control of Stratified Combustion of EGR Gas with Air-Fuel
Mixture)
[0075] It should be noted that with the internal combustion engine
1 according to the present embodiment, when the combustion is
carried out by introducing the EGR gas into the combustion chamber
4, the stratified combustion is performed in the combustion chamber
4 by the stratification of the EGR gas and the air-fuel mixture, in
order to increase the quantity of EGR gas to be supplied to the
combustion chamber 4. By performing the stratified combustion,
decrease of NOx in the exhaust gas and improvement of the fuel
consumption can be achieved.
[0076] When the stratified combustion is carried out by introducing
the EGR gas, the fresh air is supercharged by the compressor 16a of
the turbocharger 16, the fresh air blocking valve 13 is closed to
block inflow of the fresh air into the first intake port 5a, the
first intake valve 8a is opened by the variable valve mechanism 10
before opening of the second take valve 8b, and, thereafter, the
second intake valve 8b is opened.
[0077] Specifically, when the stratified combustion is carried out,
the fresh air is supercharged by the compressor 16a, the fresh air
blocking valve 13 is closed to block inflow of the fresh air into
the first intake port 5a, and, at the same time, the EGR valve 24
is opened to have the EGR gas flow into the first intake port 5a.
As shown in FIG. 3, the first intake valve 8a is opened by the
variable valve mechanism 10 immediately before the intake stroke,
and the second intake valve 8b is opened about the time when the
first intake valve 8a is closed. FIG. 3 is a diagram showing an
example of valve timing of the intake valves and the exhaust valves
at the time of stratified combustion, and a pressure in the
cylinder and a supercharging pressure at that time. The lift
quantity of the first intake valve 8a is about a half of the lift
quantity of the second intake valve 8b, because the EGR gas is so
supplied to be combustible in the combustion chamber 4.
[0078] Further, the first fuel injection valve 11a provided in the
first intake port 5a is allowed to pause, and the fuel is injected
only from the second fuel injection valve 11b provided in the
second intake port 5b. Due to this, the air-fuel mixture, which
comprises a mixture of the fresh air and the fuel, is to flow into
the second intake port 5b.
[0079] The ECU 26, which performs such control, corresponds to the
control unit of the present invention.
[0080] In this way, the fresh air blocking valve 13 is closed to
block the fresh air to flow into the first intake port 5a and the
EGR gas is flowed into the first intake port 5a, then the first
intake valve 8a is opened by the variable valve mechanism 10 before
opening of the second intake valve 8b, thereby the EGR gas which
flows through the first intake port 5a first flows into the
combustion chamber 4. This EGR gas, by flowing-in from the first
intake port 5a located at one side of the combustion chamber 4,
descends with the descending of the piston 3, while forming the
swirl flow, in the combustion chamber 4. Since the second intake
valve 8b is opened by the variable valve mechanism 10, the air-fuel
mixture flowing through the second intake port 5b flows into the
combustion chamber 4. This air-fuel mixture, by flowing-in from the
second intake port 5b located at the other side of the combustion
chamber 4, constitutes in the combustion chamber 4 a layer in which
the swirl flow is formed above the EGR gas which flowed therein
first. Thus, in the combustion chamber 4, as shown in FIG. 4, the
stratification can be achieved which comprises the EGR gas layer as
the lower layer and the air-fuel mixture layer as the upper layer.
FIG. 4 is a diagram showing, in the combustion chamber 4, the
stratified state in which the EGR gas layer is the lower layer and
the air-fuel mixture layer is the upper layer.
[0081] Here, as shown in FIG. 3, the valve opening period of time
of the second intake valve 8b may be included in the compression
stroke. With the ordinary internal combustion engine, during the
compression stroke, the piston ascends so that the volume of the
combustion chamber becomes smaller and the inner pressure of the
cylinder is increased, thereby if the intake valves are opened
there will be a possibility that the gas in the combustion chamber
would be caused to flow backward. However, with the present
embodiment, the fresh air is supercharged, and the supercharging
pressure of the fresh air to be supercharged by the compressor 16a,
is made higher than the inner pressure of the cylinder of the
internal combustion engine 1 during the period of time from closing
of the first intake valve 8a to the closing of the second intake
valve 8b. Whereby the supercharged air-fuel mixture flows into the
combustion chamber 4, without being caused to flow backward by
forcibly pushed by the inner pressure of the cylinder of the
internal combustion engine 1. Further, the gas in the combustion
chamber 4 is not caused to flow backward toward the second intake
port 5b.
[0082] When the engine load is high as the operation state of the
internal combustion engine 1 such as the one shown in FIG. 3,
consequently, it becomes difficult for the air-fuel mixture, which
flows in the combustion chamber 4 after the EGR gas, to flow into
the combustion chamber 4 with the negative pressure by the
descending of the piston 3 during the intake stroke. However, with
the present embodiment, the fresh air is supercharged by the
compressor 16a, thereby the air-fuel mixture can flow into the
combustion chamber 4 by being supercharged, not only during the
intake stroke, but also during the compression stroke. Hence, even
the engine load is high, the stratification of the EGR gas and the
air-fuel mixture can be achieved without deteriorating the intake
efficiency, and, at the same time, the EGR gas can be introduced in
a large quantity. Thus, in the case of WOT (full load) as the case
where the engine load is high, the EGR gas can be introduced.
[0083] Further, the air-fuel mixture which flows into the
combustion chamber 4 from the second intake port 5b forms the swirl
flow in the later half of the intake stroke or during the
compression stroke. Because of this, a period of time from forming
the swirl flow by the air-fuel mixture in the combustion chamber 4
to ignition is short, thereby the stratified state of the
combustion chamber 4 is easy to be maintained until ignition.
Hence, during the compression stroke, it is difficult for causing a
tumble flow in the combustion chamber 4, so that the stratified
state is difficult to be destroyed by the tumble flow, resulting in
exhibiting the effect of the stratification to the maximum.
[0084] Moreover, with the present embodiment, the EGR passage 23
connects the exhaust pipe 15 at the downstream from the turbine 16b
of the turbocharger 16 with the EGR gas supply port 12. The EGR gas
which is the part of the exhaust gas of the exhaust pipe 15 at the
downstream of the turbine 16b of the turbocharger 16, has its
temperature and pressure dropped, as it is after the EGR gas
performed the driving of the turbine 16b. With the present
embodiment, this EGR gas is flowed into the combustion chamber 4 by
the negative pressure caused by the descending of the piston 3 in
the intake stroke from the beginning of the intake stroke. At this
time, the negative pressure is secured sufficiently so that even
this EGR gas having the temperature and the pressure being dropped
is enough to be appropriately supplied to the combustion chamber 4.
By the use of this EGR gas, rising of the intake temperature is
suppressed, thereby reducing of the charging efficiency caused by a
high intake temperature can be suppressed.
[0085] It should be noted that in the case where the operation
state of the internal combustion engine 1 is such that the
stratified combustion is not performed and the requesting torque is
high and the engine load is high, the non-stratified combustion is
performed. In performing this non-stratified combustion, the EGR
valve 24 is closed to stop supplying of the EGR gas, the fresh air
blocking valve 13 is opened, the fuel is injected from the two fuel
injection valves, that is, the first and the second fuel injection
valves 11a and 11b, and, as shown in FIG. 5, the first intake valve
8a and the second intake valve 8b are set to the same lift quantity
and the same timing by the variable valve mechanism 10. FIG. 5 is a
diagram showing an example of the valve timing of the intake valve
and the exhaust valve at the time of non-stratified combustion.
[0086] (Combustion Control Routine)
[0087] A description will be made of a combustion control routine
of the internal combustion engine 1 based on the flow chart shown
in FIG. 6. FIG. 6 is a flow chart showing the combustion control
routine of the internal combustion engine 1. This routine is
executed by the ECU 26 repeatedly at every predetermined time.
[0088] Upon starting of the routine shown in FIG. 6, it is
determined in S101 as to whether or not there is a request for
performing the stratified combustion of the EGR gas and the
air-fuel mixture. As the operation state of the internal combustion
engine 1, in which the stratified combustion should be performed,
is in the region where, for example, the engine load is in the
order of a medium load thereby desirable to achieve saving of the
fuel consumption. The region, where the stratified combustion
should be performed, is mapped in advance, and the engine
revolution speed and the engine load, which can be obtained from
outputs of the crank position sensor 27 and the accelerator opening
degree sensor 28, are incorporated in the map, thereby the
determination of whether or not there is the request for performing
the stratified combustion. When, in S101, it is determined
affirmative that there is the request for performing the stratified
combustion, the routine shifts to S102. When, in S101, it is
determined negative that there is no request for performing the
stratified combustion, the routine shifts to S110.
[0089] In S102, the EGR valve 24 is opened, the fresh air blocking
valve 13 is closed and the fuel is injected from only the second
fuel injection valve 11b provided in the second intake port 5b. The
first fuel injection valve 11a provided in the first intake port 5a
is in a pause.
[0090] In S103, the lift quantity and the opening and closing
property of the valve timing of the first intake valve 8a and the
second intake valve 8b are changed by the variable valve mechanism
10 for the stratified combustion. Specifically, the opening timing
of the second intake valve 8b is lagged until about the first
intake valve 8a is closed, so as to have the first intake valve 8a
opened before opening of the second intake valve 8b, and,
thereafter, the second intake valve 8b is opened. At this time, the
lift quantity of the first intake valve 8a is also changed to about
half of the lift quantity of the second intake valve 8b.
[0091] In S104, the maximum cylinder pressure mcp of the internal
combustion engine 1 during a period from closing of the first
intake valve 8a to closing of the second intake valve 8b at the
time of stratified combustion, is calculated. This maximum cylinder
pressure mcp is calculated based on the quantity of the EGR gas
obtained from the opening degree of the EGR valve 24, the valve
timing and the lift quantity of the first intake valve 8a and the
second intake valve 8b, the engine revolution speed and the crank
angle.
[0092] In S105, it is determined whether or not the supercharge
pressure bp detected by the pressure sensor 20 of the surge tank 19
is larger than the maximum cylinder pressure mcp calculated in
S104. When, in S105, it is determined affirmative that the
supercharge pressure bp is larger than the maximum cylinder mcp
calculated in S104, the routine shifts to S107. On the other hand,
when, in S105, it is determined negative that the supercharge
pressure bp is not larger than the maximum cylinder pressure mcp,
the routine shifts to S106.
[0093] In S106, the fresh air is supercharged by the compressor
16a, thereby to increase the supercharge pressure bp.
[0094] In S107, it is determined whether or not the requesting
torque deto is larger than the actual torque trto. The requesting
torque deto can be obtained from the output of the accelerator
opening degree sensor 28. The actual torque trto can be obtained
from the fuel injection quantity of the second fuel injection valve
11b provided in the second intake port 5b. When, in S107, it is
determined affirmative that the requesting torque deto is larger
than the actual torque trto, the routine shifts to S108. On the
other hand, when, in S107, it is determined negative that the
requesting torque deto is not larger than the actual torque trto,
the routine shifts to S109.
[0095] In S108, the intake quantity is increased. The increase of
the intake quantity is made in such manner that, for example, the
opening degree of the throttle valve 17 may be made larger, the
valve timing of the first intake valve 8a and the second intake
valve 8b may be advanced, the lift quantity of the first intake
valve 8a and the second intake valve 8b may be made larger, and the
supercharge pressure bp may be raised. After this step, this
routine is finished for the time being.
[0096] In S109, the intake quantity is decreased. The decrease of
the intake quantity is made in such manner that, for example, the
opening degree of the throttle valve 17 may be made smaller, the
valve timing of the first intake valve 8a and the second intake
valve 8b may be lagged, and the lift quantity of the first intake
valve 8a and the second intake valve 8b may be made smaller. After
this step, this routine is finished for the time being.
[0097] On the other hand, in S110, in order to perform the
non-stratified combustion, the EGR valve 24 is closed, the fresh
air blocking valve 13 is opened, and the fuel injections are made
by the first and the second fuel injection valves 11a and 11b
respectively provided in the first intake port 5a and the second
intake port 5b. After this step, this routine is finished for the
time being.
[0098] With the present routine as described above, the stratified
combustion and the non-stratified combustion can be switched
between them.
[0099] (Others)
[0100] It should be noted that with the present embodiment, the EGR
passage 23 connects the exhaust pipe 15 at the downstream from the
turbine 16b of the turbocharger 16 with the EGR gas supply port 12.
Thus, by using the EGR gas in which the temperature and the
pressure are dropped, increase of the intake temperature is
suppressed and the decrease of the charging efficiency caused by
the high intake temperature is suppressed. However, the present
invention is not limited to this. FIG. 7 is a diagram showing a
schematic structure of an internal combustion engine according to
another example of the embodiment 1 and its intake system and
exhaust system. The EGR passage 23 may, as shown in FIG. 7,
connects the exhaust pipe 15 at the upstream from the turbine 16b
of the turbocharger 16 with the EGR gas supply port 12. In this
way, a part of the exhaust gas discharged from the internal
combustion engine 1 and having a high back pressure may be used as
the EGR gas, thereby the EGR gas can be sent into the internal
combustion engine 1 in a large quantity and at a high pressure.
[0101] Further, with the present embodiment, the fuel injection
valves are provided in the first intake port and the second intake
port. However, the embodiment is not limited to this. FIG. 8 is a
diagram showing a schematic structure of an internal combustion
engine according to another example of the embodiment 1. The fuel
injection valve 11 may be, as shown in FIG. 8, provided at an
oblique upper portion of the cylinder 2, and it may perform a
cylinder injection. In this case, at the time of performing the
stratified combustion, the layer of the fresh air, which is the
upper layer, is formed above the layer of the EGR gas, which is the
lower layer. Thus, at the time of performing the stratified
combustion, the fuel injection valve 11 sets an injection axis line
so as to inject the fuel to only the fresh air of the fresh air
layer, which is the upper layer. In this way, providing only one
fuel injection valve is sufficient, thereby an increase of cost can
be suppressed.
[0102] Further, with the present embodiment, a turbocharger is used
as the supercharger. But the present invention is not limited to
this. The present invention may use a supercharger as the
supercharger.
Embodiment 2
[0103] In an embodiment 2, a first intake port and a second intake
port use a helical port or a tangential port so that the intake air
which flow into the combustion chamber forms the swirl flow in the
same direction. All other structures are the same with that of the
embodiment 1, so that the description thereof will be omitted.
[0104] FIG. 9 is a diagram showing a state in which the helical
port or the tangential port is used for the first intake port 5a
and the second intake port 5b according to the present embodiment.
FIG. 9(a) is a diagram showing a double helical intake port, and
FIG. 9(b) is a diagram showing a double tangential intake port. As
shown in FIG. 9, the first intake port 5a and the second intake
port 5b are the helical port or the tangential port, thereby the
intake air, which has flowed into the combustion chamber 4, forms
the swirl flow in the same direction. In addition to the structure
shown in FIG. 9, a combination wherein one intake port is the
helical port and the other intake port is the tangential port, may
be used.
[0105] In this way, when the stratified combustion is performed,
the lower layer forming the swirl flow of the EGR gas which has
flowed-in first and the upper layer forming the swirl flow of the
air-fuel mixture above the lower layer are whirling as the swirl
flows in the same direction in the combustion chamber 4, as shown
in FIG. 10. FIG. 10 is a diagram showing the stratified state
wherein the layer of the EGR gas is the lower layer and the layer
of the air-fuel mixture is the upper layer. As a result, it is
difficult to produce frictions at the boundary surface between the
upper layer and the lower layer, and also it is difficult to cause
mixing of the EGR gas with the air-fuel mixture, and, hence, the
stratified state can be maintained for as long as possible. With
this, coupled with the fact that the swirl flow of the upper layer
is formed in the later half of the intake stroke and in the
compression stroke, the stratified state can be maintained until
the ignition time.
Embodiment 3
[0106] In an embodiment 3, at the time of performing the stratified
combustion, and in the case where the air-fuel mixture flowing
through the second intake port is not required to be flowed into
the combustion chamber in the compression stroke, the compressor of
the turbocharger is not operated and the fresh air is not
supercharged. All other structures are the same with that of the
embodiment 1, so that the description thereof will be omitted.
[0107] In the present embodiment, at the time of performing the
stratified combustion, and in the case where the air-fuel mixture
flowing through the second intake port 5b is to flow into the
combustion chamber 4 in the compression stroke, the control which
is the same as that of the embodiment 1 is carried out. However, at
the time of performing the stratified combustion and in the case
where the air-fuel mixture which flows through the second intake
port 5b is not required to be flowed into the combustion chamber 4
in the compression stroke, the compressor 16a of the turbocharger
16 is not operated and the fresh air is not supercharged, wherein
the fresh air blocking valve 13 is closed to block inflow of the
fresh air into the first intake port 5a, the first intake valve 8a
is opened before opening of the second intake valve 8b, and
thereafter the second intake valve 8b is opened, by the variable
valve mechanism 10.
[0108] Specifically, at the time of performing the stratified
combustion, and in the case where the air-fuel mixture flowing
through the second intake port 5b is not required to be flowed into
the combustion chamber 4 in the compression stroke, the fresh air
is not supercharged by the compressor 16a, the fresh air blocking
valve 13 is closed to block the inflow of the fresh air into the
first intake port 5a, and, at the same time, the EGR valve 24 is
opened to allow the EGR gas to flow into the first intake port 5a.
Then, as shown in FIG. 11, the first intake valve 8a is opened from
immediately before the intake stroke by the variable valve
mechanism 10, and the second intake valve 8b is opened about the
time when the first intake valve 8a is closed. Then, the second
intake valve 8b is closed immediately after the compression stroke.
FIG. 11 is a diagram showing an example of the valve timing of the
intake valve and the exhaust valve at the time of performing the
stratified combustion when the air-fuel mixture flowing through the
second intake port is not required to be flowed into the combustion
chamber in the compression stroke. The lift quantities of the first
intake valve 8a and the second intake valve 8b are both small. The
lift quantity of the first intake valve 8a is about half of the
lift quantity of the second intake valve 8b, because it supplies
the EGR gas to be combustible in the combustion chamber 4. Further,
the first fuel injection valve 11a provided in the first intake
port 5a is paused, and the fuel is injected only from the second
fuel injection valve 11b provided in the second intake port 5b.
Because of this, the air-fuel mixture comprising the fresh air and
the fuel flows through the second intake port 5b.
[0109] The ECU 26 which performs these controls is corresponding to
the control unit of the present invention.
[0110] When the air-fuel mixture is not required to flow into the
combustion chamber 4 in the compression stroke as in the case where
the engine load is low as the operation state of the internal
combustion engine 1, as shown in FIG. 11, the air-fuel mixture,
which inflows after the EGR gas, can be allowed to flow into the
combustion chamber 4 by the negative pressure due to the descending
of the piston in the intake stroke. Whereby, when the air-fuel
mixture is not required to flow into the combustion chamber 4 in
the compression stroke, the fresh air is not supercharged by the
compressor 16a so that the energy corresponding to the energy which
might have been used by the turbocharger 16 can be reduced,
resulting in saving energy. Namely, there is no need to increase
the output of the internal combustion engine 1 to supercharge the
fresh air by the turbocharger 16, and, hence, improving the fuel
consumption.
Embodiment 4
[0111] In an embodiment 4, the fresh air blocking valve is a three
way valve that switches the intake air to flow through the first
intake port to be either the fresh air, which inflows from the
upstream of the first intake port, or the EGR gas, which inflows
from the EGR gas supply port. All other structures are the same
with that of the embodiment 1, so that the description thereof will
be omitted.
[0112] FIG. 12 is a diagram showing a schematic structure of an
internal combustion engine according to the present embodiment and
its intake system and exhaust system. As shown in FIG. 12, the EGR
gas supply port 12 is located at the position of the first intake
port 5a which is provided with the fresh air blocking valve 13. The
fresh air blocking valve 13 switches the intake air to flow through
the first intake port 5a to be either the fresh air which inflows
from the upstream of the first intake port 5a, or the EGR gas which
inflows from the EGR gas supply port 12. The fresh air blocking
valve 13 of the present embodiment is the three way valve. Further,
the EGR apparatus 22 does not have the EGR valve. The control of
the quantity of the EGR gas is performed by valve opening timing
and the lift quantity of the first intake valve 8a.
[0113] In this way, that is, the quantity of the EGR gas is
controlled by the valve opening timing and the lift quantity of the
first intake valve 8a, it is not required to provide the EGR valve
to the EGR apparatus 22. Whereby, the control of the quantity of
the EGR gas can be simplified, and, also, due to not requiring the
EGR valve, the number of parts is reduced, resulting in effecting
the cost-down.
[0114] Further, the control of the quantity of the EGR gas is
performed by the first intake valve 8a, the distance between the
part which controls the quantity of the EGR gas and the combustion
chamber 4 becomes zero, so that there is no delay of response by
the EGR gas, a misfire and torque fluctuations of the internal
combustion engine 1 are suppressed, resulting in stabilizing of the
drivability.
[0115] FIG. 13 is a diagram showing a pattern of selecting the
stratified combustion of the EGR gas and the air-fuel mixture, and
the non-stratified combustion where the EGR gas is not introduced,
whichever corresponds to an operation state of the internal
combustion engine. With the internal combustion engine 1 of the
present embodiment, the selection is made, as shown in FIG. 13,
between the stratified combustion and the non-stratified
combustion, according to the operation state. In FIG. 13, the
horizontal axis represents the engine revolution speed of the
internal combustion engine 1, and the vertical axis represents the
engine load of the internal combustion engine 1.
[0116] As indicated by an arrow mark "A" in FIG. 13, when switching
is made from the stratified combustion where the EGR gas is
introduced in the operation state of at least either the state
where the engine load is high or the state where the engine
revolution speed is high, to the non-stratified combustion where
the requesting torque is high and the EGR gas is not introduced, it
is desirable that the switching or shifting from the stratified
combustion to the non-stratified combustion without causing the
delay in response; and a misfire, torque fluctuations and
fluctuations in steps of torque of the internal combustion engine
1.
[0117] Thus, in the structure of the present embodiment, the volume
of the first intake port 5a from the fresh air blocking valve 13 to
the combustion chamber 4 is set to substantially equal to the
quantity of the EGR gas supplied to the combustion chamber 4 at the
time of performing the stratified combustion where the EGR gas is
introduced in the operation state of at least either the state
where the engine load is high or the state where the engine
revolution speed is high. Hence, when the stratified combustion is
performed by introducing the EGR gas in the operation state of at
least either the state where the engine load is high or the state
where the engine revolution speed is high, the EGR gas of the first
intake port 5a from the fresh air blocking valve 13 to the
combustion chamber 4 is has been used and exhausted by the
combustion of one cycle.
[0118] FIG. 14 is a diagram showing a control timing when switching
is made from the stratified combustion where the EGR gas is
introduced in the operation state of at least either the state
where the engine load is high or the state where the engine
revolution speed is high, to the non-stratified combustion where
the requesting torque is high and the EGR gas is not introduced.
When switching is made from the stratified combustion to the
non-stratified combustion as indicated by the arrow mark "A" in
FIG. 13, there is, first, a request for switching (t1 in FIG. 14),
and when the cylinder #3, which has entered into the intake stroke
first after the request for switching, starts flowing the intake
air into the combustion chamber 4 (t2 in FIG. 14), the intake air
to flow through the first intake port 5a is switched, by the fresh
air blocking valve 13, to the fresh air flowing-in from the
upstream of the first intake port 5a. Thereafter, from the time
when inflow of the intake air into the combustion chamber 4 in the
first one cycle of cylinders (#1, #2 and #4), other than the
cylinder #3, which had entered into the intake stroke first, has
been completed (t3 in FIG. 14), the opening and closing properties
of the first intake valve 8a and the second intake valve 8b are
changed by the variable valve mechanism 10, as shown in FIG.
15.
[0119] The ECU 26 that performs such controls corresponds to the
control unit of the present invention.
[0120] FIG. 15 is diagram showing an example of valve timing of the
intake valve and the exhaust valve when switching is made from the
stratified combustion where the EGR gas is introduced in the
operation state of at least either the state where the engine load
is high or the state where the engine revolution speed is high, to
the non-stratified combustion where the requesting torque is high
and the EGR gas is not introduced. At the time of switching, as
indicated by arrow marks in FIG. 15, the first intake valve 8a
increases the lift quantity while lagging the valve timing a
little, and the second intake valve 8b advances the valve timing.
Then, as indicated by a broken line in FIG. 15, the first intake
valve 8a and the second intake valve 8b are made to have the same
lift quantity and the same timing, thereby to perform the
non-stratified combustion (refer to FIG. 5).
[0121] In this way, since the volume of the first intake port 5a is
set as described above, only the combustion of one cycle of all of
the cylinders after the switching request becomes the stratified
combustion, and, thereafter, the fresh air flows through the first
intake port 5a, so that the next and subsequent combustions will be
the non-stratified combustion. As a result, the shifting from the
stratified combustion to the non-stratified combustion can be
effected without causing a response delay, and a misfire, torque
fluctuations and fluctuations in the steps of torque.
Embodiment 5
[0122] In an embodiment 5, when the non-stratified combustion is
performed in the state of low engine load wherein the EGR gas is
not introduced, for example, as in the idling state, the first
intake valve is maintained being closed by the variable valve
mechanism. All other structures are the same with that of the
embodiment 1, so that the description thereof will be omitted.
[0123] When the non-stratified combustion is performed in the state
of low engine load wherein the EGR gas is not introduced, for
example, as in the idling state, it is desirable to form the swirl
flow in the combustion chamber 4 to stabilize the combustion. When
switching is made from the non-stratified combustion to the
stratified combustion where the EGR gas is introduced, it is
desirable to suppress causing of steps of torque, which might have
been caused by steps produced in the quantity of the air-fuel
mixture between before and after the switching.
[0124] Thus, when the non-stratified combustion is performed in the
state of low engine load wherein the EGR gas is not introduced, for
example, as in the idling state, the first intake valve 8a is
maintained being closed by the variable valve mechanism 10.
[0125] Specifically, when the non-stratified combustion is
performed, the fresh air is not supercharged by the compressor 16a,
the fresh air blocking valve 13 is closed to block inflow of the
fresh air into the first intake port 5a, and, at the same time, the
EGR valve 24 is opened to allow the EGR gas to flow into the first
intake port 5a. Then, as shown in FIG. 16, the first intake valve
8a is maintained being closed by the variable valve mechanism 10,
and the second intake valve 8b is opened. FIG. 16 is a diagram
showing an example of valve timing of the intake valve and the
exhaust valve at the time of non-stratified combustion in the state
of low engine load where the EGR gas is not introduced. Further,
the first fuel injection valve 11a provided in the first intake
port 5a is paused, and the fuel is injected only from the second
fuel injection valve 11b provided in the second take port 5b.
Thereby, the air-fuel mixture comprising the fresh air and the fuel
is to flow through the second intake port 5b.
[0126] The ECU 26 that performs such controls corresponds to the
control unit of the present invention.
[0127] Whereby, when the non-stratified combustion is performed in
the state of low engine load of the internal combustion engine 1
wherein the EGR gas is not introduced, the second intake valve 8b,
which is one of the intake valves, is opened to allow the air-fuel
mixture to flow into the combustion chamber. Consequently, a strong
swirl flow can be formed in the combustion chamber 4 and the
combustion is stabilized.
[0128] Then, when switching is made from the non-stratified
combustion to the stratified combustion wherein the EGR gas is
introduced, the first intake valve 8a is opened to allow inflow of
the EGR gas from the first intake port 5a, and, at the same time,
the second intake valve 8b is opened, the same as was before the
switching to allow inflow of the air-fuel mixture in the same
quantity from the second intake port 5b. At this time, the valve
opening time of the first intake valve 8a by the variable valve
mechanism 10 is slightly advanced, and, at the same time, the valve
opening time of the second intake valve 8b is lagged, so that the
second intake valve 8b is opened about the time when the first
intake valve 8a is closed. Hence, the quantity of the air-fuel
mixture supplied to the combustion chamber 4 is not changed between
before and after the switching, so that the shifting from the
non-stratified combustion to the stratified combustion can be
effected without causing steps in torque.
[0129] The above-described respective embodiments may be combined
to varieties in as many as possible. Further, the combustion
control apparatus for the internal combustion engine according to
the present invention is not limited to the above-described
embodiments, but various modifications may be added within the
scope of not deviating from the gist of the present invention.
DESCRIPTION OF REFERENCE NUMERALS AND SYMBOLS
[0130] 1: internal combustion engine
[0131] 2: cylinder
[0132] 3: piston
[0133] 4: combustion chamber
[0134] 5a: first intake port
[0135] 5b: second intake port
[0136] 6a: first exhaust port
[0137] 6b: second exhaust port
[0138] 7: spark plug
[0139] 8a: first intake valve
[0140] 8b: second intake valve
[0141] 9a: first exhaust valve
[0142] 9b: second exhaust valve
[0143] 10: variable valve mechanism
[0144] 11: fuel injection valve
[0145] 11a: first fuel injection valve
[0146] 11b: second fuel injection valve
[0147] 12: EGR gas supply port
[0148] 13: fresh air blocking valve
[0149] 14: intake pipe
[0150] 15: exhaust pipe
[0151] 16: turbocharger
[0152] 16a: compressor
[0153] 16b: turbine
[0154] 16c: waste gate valve
[0155] 17: throttle valve
[0156] 18: intercooler
[0157] 19: surge tank
[0158] 20: pressure sensor
[0159] 21: oxidation catalyst
[0160] 22: EGR apparatus
[0161] 23: EGR passage
[0162] 24: EGR valve
[0163] 25: EGR cooler
[0164] 26: ECU
[0165] 27: crank position sensor
[0166] 28: Accelerator opening degree sensor
* * * * *